Electronic devices are enabled to communicate with other electronic devices using wired and wireless (or radio) communication techniques. The electronic devices may transmit and receive radio signals using an antenna. The antenna may be designed to transmit and receive electromagnetic signals. The antenna may comprise physical elements such as conductors of various shapes and sizes. While transmitting, the antenna may generate a radiating electromagnetic field in response to an applied alternating voltage or current. The radiating electromagnetic field may form patterns (radiating patterns), which provide an insight into the strength of the radiating electromagnetic field in a specific direction. While receiving, the antenna placed in an electromagnetic field may allow the electromagnetic field to induce an alternating current in the antenna and a voltage between the terminals of the antenna.
Antennas may be classified in numerous ways. Based on the radiation pattern generated by the antennas, the antennas may be classified, for example, as omni-directional antennas and directional antennas. Based on the bandwidth in which the antennas may operate, the antennas may be classified as narrow-band, multi-band, and broadband antenna. Omni-directional antennas may be well suited for portable devices such as laptops, mobile internet devices, and cellular devices. Broadband antennas may be suited for applications such as ultra wide-band (UWB) or multiple radios using a single antenna. Omni-directional broadband antennas are essential, for example, in cognitive radio systems. The existing omni-directional antennas operate over small bandwidths, typically, 10% of the lowest operating frequency and these antennas operate at about 50% efficiency.